微重力条件下生长GaAs单晶的电学和光学性质研究

用多种实验手段分别对地面和太空生长的掺Te砷化镓单晶的电学、光学均匀性和深能级行为进行了实验研究.初步结果表明:在太空进行再生长的GaAs单晶电子浓度比原地面生长的籽晶小一个数量级,电子浓度由地面晶体到太空晶体的过渡是陡变的;DLTS测量发现太空单晶中存在两个电子陷阱,分别位于导带下0.27eV和0.60eV处,深能级密度为浅施主N_D的10~(-3)-10~(-4);少子注入未观察到空穴陷阱;用太空GaAs单晶为衬底制备的25个单异质结(SH)二极管,具有一致的I-V和发光特性,这反映了太空晶体的均匀性优于地面晶体.此外,还对太空生长GaAs单晶电子浓度降低的可能原因、深能级行为以及太空生长高质量晶体的前景作讨论.

Study on Electrical and Optical Properties of GaAs Grown from Melt under Microgravity Conditions

The electrical and optical properties of Te-doped GaAs grown in space and on the earthrespectively were systematically studied by using Hall, C-V, EL, PL and DLTS techniques.Theresults demostrated that (1) Free carrier concentration of the regrown space-crystal is one ma-gnitude less than that of the ground-crystal. (2) There is a transition region between the spaceand ground grown materials in which the electron concentration (variation from the groundto the space) decreases gradually first,then goes down abruptly to the crystal grown in space.This is caused by a special crystal growth condition in space. (3) DLTS measurement on thespace samples revealed two deep electron traps with very low concentrations (N_t/N_d<0.0001)which located below the conduction band 0.27 eV and 0.60 eV respectively and the hole trapsare not seen in these samples. (4) The I-V characteristics and EL intensities of the singleheterojunction diodes grown on the substrate of the space material by using LPE methodclearly showed the similarity each other.This indicated that the space crystal had a verygood electrical and optical homogeneity.Ths is because i) thermal convections in the meltand solution convections are suppressed under microgravity conditions, ii) The stoichiometryfluctuations caused by thermal convections in the melt and in the vapor phase as well as so-lute convections can be also eliminated in space.